Cooling system fan hydraulic speed control



Sept. 9, 1969 J. E. wuNDx-:R

COOLING SYSTEM FAN HYDRAULIC SPEED CONTROL Filed March 27, 1968 sm N ESE /m/ Elvron JOHN E. WUNDER HIS ATTORNEY United States Patent O U.S. Cl. 62--184 8 Claims ABSTRACT F THE DISCLOSURE A control system for a hydraulic motor rotating a condenser `fan in a vapor cycle cooling system wherein hydraulic uid is supplied to the motor in amounts varying with variations in condenser head pressure.

Although not so limited, the invention has particular reference to refrigeration or cooling systems contained in an aircraft service trailer or the like required to have a large cooling capacity but which on account of space limitations require that accessory equipment and controls be as compact and light in weight as possible. Vapor cycle cooling or refrigeration systems commonly include a fan which when rotated induces a flow of ambient air over the condenser for cooling purposes. In a trailer or like environment the use of an electric motor to rotate the condenser fan is undesirable since the powering thereof would require an impracticably large generator to be included in the trailer equipment. An object of the instant invention is to provide for hydraulic operation of a condenser fan, it being an attendant object in this connection to provide hydraulic motor means and controls thereof of such compact size and simplicity as to be readily embodied in an environment having restricted space requirements.

It is desirable, in systems of the class described, to change the speed of fan operation to suit changing heat load requirements or in consequence of changing ambient temperatures, or both. While in an electric motor driven fan system this may relatively easily be arrived at through use of a multi-speed electric motor the achieving of like lresults with a hydraulic motor is less obvious. Moreover, an eifective cooling system suggests the desirability of a number of different fan speed operations preferably directly related to a changing pressure condition of the refrigerant. It is accordingly another object of this invention to introduce a system of controls for a hydraulic condenser fan motor by which the speed of operation of the motor may be varied infinitely with the system imparting a capability to the motor of constant operation at a selected speed. Still further, it is an object to carry out control operations automatically in response to a changing refrigerant pressure, for example the condenser head pressure.

Other objects and structural details of the invention Will appear from tthe following description, when read in connection with the accompanying drawing, which is a diagrammatic view of a cooling system with hydraulic controls in accordance with an illustrated embodiment of the invention.

Referring to the drawing, the components of a vapor cycle refrigeration system include an evaporator 10, a compressor 11, a condenser 12, a receiver 13, and an expansion valve 14, all interconnected in a closed circuit or loop as represented by a refrigerant flow line 15. Refrigerant gas is drawn from evaporator into compressor 11 and delivered under pressure to the condenser 12. A flow of ambient air over or through condenser 12 is induced by rotation of a fan 16, the air coming into heat transfer ICC relation within the condenser to the refrigerant supplied thereto, cooling the refrigerant and reducing it to a greater or lesser extent to condensate form. The condensate or a mixture of condensate and vapor continues on beyond condenser 12 to receiver 13 and thence to expansion valve 14 where the refrigerant is supplied under controlled pressure conditions to the evaporator 10. It is of course desirable that the outlet pressure of the condenser, or what may be considered condenser head pressure, be at a sufficiently high value that expansion valve 14 may operate adequately to supply refrigerant to evaporator 10. Desirably the condenser head pressure is maintained at a substantially uniform value despite variations in imposed heat load and despite variations in temperature of the ambient air drawn across the condenser. A method of control looking toward the maintenance of such uniform pressure is to vary the speed of rotation of fan 16. An increase in fan speed accelerates the rate of cooling within the condenser and tends to compensate for an increase in heat load or an increase in ambient air temperature or both. A decrease in fan speed reduces the rate of flow of cooling air through the condenser and thereby tends to compensate for a decrease in applied heat load or a decrease in ambient air temperature, or both.

The condenser fan 16 is, in accordance with the instant invention, rotatively driven by a hydraulic motor 17 which is in a hydraulic circuit further including a reservoir 18 and a pump 19. The pump 19 has a pressure side connected by a line 21 to the motor 17. The pump 19 has a suction side connected to the reservoir 18 and through it to the hydraulic motor 1'7 by a low pressure return line 22. The hydraulic motor 17 drives fan 16 through a projecting shaft 23. The hydraulic pump 19 may be driven in any convenient manner, as through a projecting shaft 24 on which is a pulley 25. A belt 26 connects pulley 25 and another pulley 27 itself driven from a prime mover by a shaft 28. In response to operation of the hydraulic pump 19, liquid, which will hereinafter for convenience be referred to as oil, is drawn from reservoir 18 and directed under pressure through a lter 20 to motor 17 The oil leaves motor 17 by way of low pressure return line 22 and is conducted thereby back to reservoir 18. The pump 19, at a given speed of operation, tends to pump a constant quantity of oil to the motor 17 at a pressure which is a function of the pump operation and of various restrictions to flow of the pumped oil. The speed of operation of the motor 17, and thereby the speed of rotation of the fan 16, may thus be changed by varying the amount of oil flowing to motor 17, independently of pump operation.

In the hydraulic system, the pressure line 21 and return line 22 are interconnected by a line 29 in by-passing relation to motor 17. Within line 29 is a chamber 31, the lower end of which communicates directly with pressure line 21 and forms a valve seat 32. Reciprocable in the chamber 31 is a piston 33, a dependent portion of which is reduced in diameter and formed at its extremity with a tapered valve portion 34 adapted to rest in and upon seat 32. When so engaged, element 33-34- which may be considered a by-pass control valve, closes chamber 31 froml communication with pressure line 21 and hence closes by-pass 29. A compression spring 35 is received in the upper endof chamber 31 and urges control valve 33- 34 to a seated or closed position. The space occupied by spring 35, above piston portion 33 of the by-pass control valve, forms a chamber 36 which may be considered a control pressure chamber.

A passage 37 having a restriction 38 therein connects pressure line 21 to control chamber 36. The latter further is connected by a passage 39 to the lower end of a chamber 41 the bottom of which defines a valve seat 42 u through which passage 39 opens. A tapered valve element 43 is received in chamber 41 and is adapted to rest in and upon seat 42, closing communication of chamber 41 with passage 39. A compression spring 44 is interposed between valve 43 and a piston 45 reeiprocable in chamber 41. Under compression, the spring 44 exerts a pressure, variable with the longitudinal position of piston 45, to urge valve 43 to a seated or closed position. A rod 46 has its one end extending into the upper end of chamber 41 and abuts piston 45. At its other end rod 46 extends into a chamber 47 in which is a bellows 48, the said other end of rod 46 connecting to the lower end of the bellows for unison extension and retraction therewith. A spring 49 may be provided to assist in bellows retraction. The bellows 48 defines a pressure chamber 51 communieating through a passage 52 with the refrigerant flow line at a location therein to sense condenser head pressure.

In the operation of the system, condenser head pressure as variably affected by changing heat load conditions or changing ambient air temperatures, or both, is communicated through passage 52 with chamber 51 of the hydraulic system. The bellows 48 assumes a position of relative extension in chamber 47 which is thus a function of opposing forces as represented by refrigerant pressure in chamber 51 and by the inherent resistance to extension of the bellows, supplemented by compression spring 49. The passage 52 is a bridge between the refrigerant flowing circuit and the hydraulic circulating system, with bellows 48 and associated parts having the character of a transducer whereby changes in condenser head pressure in the refrigerant system may be introduced as control signals in the hydraulic system.

The rod 46 is extended and retracted as variations in condenser head pressure cause bellows 48 to move to different longitudinal positions of adjustment. Piston 45 in chamber 41 is in a following relation to rod 46, by virtue of the pressure of spring 44 and hence is repositioned in correspondence with longitudinal re-positioning of bellows 48. The result is to bring about varying stages of compression of the spring 44 and thereby to vary the resistance applied to unseating of valve 43. The latter closes against pressure in passage 39 which is the pressure of control chamber 36. When this pressure is sufficiently high, valve 43 is raised from its seat, allowing pressure from control chamber 36 to flow through passage 39 to chamber 41 and out of the chamber to by-pass 29 by way of an interconnecting passage 53. The control pressure at which valve 43 opens is determined by the degree of compression of spring 44 which in turn varies as refrigerant pressure in chamber 51 varies.

Hydraulic fluid exhausted from chamber 36 is not replenished at the same rate, due to restriction 38. Accordingly, the pressure in control chamber 36 is reduced and the -by-pass 29 opens as by-pass control valve 33-34 responds to the lowering pressure in chamber 36 by raising off of seat 32. A portion of the oil flowing through pressure line 21 to hydraulic motor 17 accordingly is diverted through by-pass 29 directly to return line 22. The amount of oil supplied motor 17 is reduced thereby. The speed of operation of the motor and consequently the speed of rotation of fan 16 is proportionately reduced.

The by-pass control valve 33-34 assumes various longitudinal positions of adjustment in accordance with the value of control pressure in chamber 36. This in turn is a function of the position of valve 43 with the response of this valve to given pressure conditions changing with the changing state of compression of spring 44. The amount of oil which may be by-passed is infinitely variable according to the disclosed system of control. In consequence the speed of operation of motor 17 is infinitely variable. Moreover, since by-pass control valve 33-34 will stabilize in any control position it may assume as a result of changing condenser head pressure, as long as such head pressure remains constant, the motor 17 will run constantly at its indicated controlled speed.

The hydraulic control system hereof has been shown in a diagrammatic form inasmuch as details of the valve mechanisms are not essential to an understanding of the invention. Further, the valve mechanisms may vary in their details without departing from the spirit and teachings of the invention. For example, the passage 37 and restriction 38 may variously be arrived at as by being a passage in a valve body of which control valve 33-34 is a part. It might also be embodied in the by-pass control valve itself as a passage extending longitudinally through th valve. The transducer in the form of bellows 48 and associated parts may have the character of an actuator connected into the refrigeration system and extending directly or by remote control to the spring compressing piston 45. Another valve, like the valve 43, might be connected in parallel to valve 43 to open independently there of in the presence of a predetermined high pressure in chamber 36.

In general, a preferred embodiment of the invention has been disclosed, but it is intended that the scope of the invention should be limited only by the claims allowed herein.

What is claimed is:

1. n a cooling system wherein an air cooled condenser is arranged in a refrigerant flowing circuit and a fan is disposed to induce when rotated a flow of air over said condenser; a hydraulic motor connected to rotate said fan, and means for operating said motor at an infinitely variable number of speeds related to and controlled by a changing pressure in said refrigerant fiowing system.

2. A system according to claim 1, wherein means are provided for supplying liquid under pressure to said motor for operation thereof, characterized in that said motor operating means includes means for by-passing varying amounts of supplied liquid to vary the speed of operation of said motor and thereby the speed of rotation of said fan.

3. A system according to claim 2, characterized by means for sensing variations in condenser head pressure, said by-passing means operating under the control of said sensing means.

4. A system according to claim 1, wherein means are provided for supplying liquid under pressure to said motor for operation thereof, characterized in that said motor operating means includes means to sense the pressure in said refrigerant fiowing circuit and extending and retracting as said pressure varies, a by-pass control valve for varying the amounts of liquid supplied to said motor, and means utilizing extension and retraction of said sensing means to control operation of said by-pass control valve.

5. A system according to claim 1, wherein means are provided for supplying liquid under pressure to said motor for operation thereof, characterized in that said motor operating means includes a valve variably positionable to by-pass variable amounts of supplied liquid, a different speed of operation of said motor and thereby a different speed of rotation of said fan resulting in each position of said valve, and means for sensing the said changing pressure in said refrigerant fiowing system and for positioning said by-pass control valve in accordance therewith.

6. A system according to claim 1, wherein said motor is in a hydraulic flow circuit further including a pump and pressure and return lines leading respectively from said pump to said motor and from said motor back to said pump and still further includes a by-pass between said pressure and return lines, characterized by a pressure responsive valve interposed in to control ow through said by-pass, pressures from said pressure line being applied to said valve in opposing opening and closing directions, and means responsive to changes in the said changing refrigerant pressure in said refrigerant fiowing system to vary the hydraulic pressure acting to close said valve.

7. A system according to claim 6, wherein the hydraulic pressure acting to close said valve is exerted in a pressure chamber in restricted communication with said pressure line, characterized in that said last named means includes transducer means utilizing changes in pressure of said changing refrigerant pressure to effect extension and retraction of an actuator, and means responsive to movement of said actuator varably to limit the high pressure value attainable in said pressure chamber.

8. A system according to claim 7, characterized in that said last named means includes another valve controlling communication of said pressure chamber with said return line and biased to a closing position, said actuator varying the degree of biasing pressure with which said other valve is urged closed.

References Cited UNITED STATES PATENTS 2,518,316 8/1950 Henney 62-215 2,952,991 9/1960 Pierre 62-184 3,402,565 9/1968 Maynard 62-183 10 MEYER PERLIN, Primary Examiner 

